﻿using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;


namespace japanese
{
    class Unility
    {
        public class TxtFileEncoding
        {
            public TxtFileEncoding()
            {
                //
                // TODO: 在此处添加构造函数逻辑
                //
            }

            /// <summary>
            /// 取得一个文本文件的编码方式。如果无法在文件头部找到有效的前导符，Encoding.Default将被返回。
            /// </summary>
            /// <param name="fileName">文件名。</param>
            /// <returns></returns>
            public static Encoding GetEncoding(string fileName)
            {
                return GetEncoding(fileName, Encoding.Default);
            }

            /// <summary>
            /// 取得一个文本文件流的编码方式。
            /// </summary>
            /// <param name="stream">文本文件流。</param>
            /// <returns></returns>
            public static Encoding GetEncoding(FileStream stream)
            {
                return GetEncoding(stream, Encoding.Default);
            }

            /// <summary>
            /// 取得一个文本文件的编码方式。
            /// </summary>
            /// <param name="fileName">文件名。</param>
            /// <param name="defaultEncoding">默认编码方式。当该方法无法从文件的头部取得有效的前导符时，将返回该编码方式。</param>
            /// <returns></returns>
            public static Encoding GetEncoding(string fileName, Encoding defaultEncoding)
            {
                FileStream fs = new FileStream(fileName, FileMode.Open);
                Encoding targetEncoding = GetEncoding(fs, defaultEncoding);
                fs.Close();
                return targetEncoding;
            }

            /// <summary>
            /// 取得一个文本文件流的编码方式。
            /// </summary>
            /// <param name="stream">文本文件流。</param>
            /// <param name="defaultEncoding">默认编码方式。当该方法无法从文件的头部取得有效的前导符时，将返回该编码方式。</param>
            /// <returns></returns>
            public static Encoding GetEncoding(FileStream stream, Encoding defaultEncoding)
            {
                Encoding targetEncoding = defaultEncoding;
                if (stream != null && stream.Length >= 2)
                {
                    //保存文件流的前4个字节
                    byte byte1 = 0;
                    byte byte2 = 0;
                    byte byte3 = 0;
                    byte byte4 = 0;
                    //保存当前Seek位置
                    long origPos = stream.Seek(0, SeekOrigin.Begin);
                    stream.Seek(0, SeekOrigin.Begin);

                    int nByte = stream.ReadByte();
                    byte1 = Convert.ToByte(nByte);
                    byte2 = Convert.ToByte(stream.ReadByte());
                    if (stream.Length >= 3)
                    {
                        byte3 = Convert.ToByte(stream.ReadByte());
                    }
                    if (stream.Length >= 4)
                    {
                        byte4 = Convert.ToByte(stream.ReadByte());
                    }

                    //根据文件流的前4个字节判断Encoding
                    //Unicode {0xFF, 0xFE};
                    //BE-Unicode {0xFE, 0xFF};
                    //UTF8 = {0xEF, 0xBB, 0xBF};
                    if (byte1 == 0xFE && byte2 == 0xFF)//UnicodeBe
                    {
                        targetEncoding = Encoding.BigEndianUnicode;
                    }
                    if (byte1 == 0xFF && byte2 == 0xFE && byte3 != 0xFF)//Unicode
                    {
                        targetEncoding = Encoding.Unicode;
                    }
                    if (byte1 == 0xEF && byte2 == 0xBB && byte3 == 0xBF)//UTF8
                    {
                        targetEncoding = Encoding.UTF8;
                    }

                    //恢复Seek位置      
                    stream.Seek(origPos, SeekOrigin.Begin);
                }
                return targetEncoding;
            }
        }
    }
}
